In the Japanese electric power industry, in April 2005, the scope of electricity retail liberalization was expanded to commercial-scale utility customers of 50 kW, and wheeling charge for electric power accommodation across a plurality of power companies will be unified. Therefore, retail wheeling to a city or plant from a remote location is expected to be actively pursued. Under these circumstances, it is important to accurately grasp the margin for sending electrical power, and to quickly cope with a possible problem by re-setting a stabilization control apparatus.
Fluctuation of an electric power system is stabilized mainly through design of an auxiliary signal of an excitation system. In a generally known method, local and wide-area fluctuations in an electric power system are stabilized by means of signal processing in which advance or delay in phase is compensated by use of a generator angular speed deviation Δω and a generator output deviation ΔP obtained from the power system (see Patent Document 1).
FIG. 25 is a diagram showing the functions of an excitation apparatus and a PSS (power system stabilizer) used for system stability control. Section (A) schematically shows the configuration of a single generator connected to an electric power system, and section (B) is a block diagram showing the details of the excitation apparatus and the PSS shown in section (A). A large number of generators are connected to the power system, and in order to stabilize each generator, a PSS is provided so as to feed-back the rotational angular speed deviation Δω or the like of the generator to be used as an auxiliary signal of the excitation apparatus, which controls the field winding voltage.
As shown in FIG. 25(B), the excitation apparatus (AVR) controls the generator terminal voltage Vt to a prescribed value Vref, and increases or decreases an excitation voltage Efd based on the deviation (Vref−Vt). The dynamic characteristics of the exciter and an excitation voltage generator which produces a voltage necessary to operate the exciter which produces the excitation voltage are shown in the respective blocks in the drawing. “s” represents a Laplacian operator. A hunting prevention section is provided so as to prevent abrupt changes in a signal.
The generator terminal voltage Vt is input from the outer terminal of the generator via a transformer for measurement, and a voltage corresponding to a prescribed value of the generator output terminal voltage is input as the prescribed value Vref. Further, a voltage Efd0/100 corresponding to a prescribed value of the excitation voltage is generated and fed to the exciter together with the voltage generated by the excitation voltage generator. The reason for the division by 100 is that in this example, the amplification ratio of the exciter is 100, and therefore, the voltage Efd0 must be adjusted by dividing it by 100 so as to match the signal level of the excitation voltage Efd.
“1.0” of an amplification section of the excitation apparatus represents the signal amplification ratio thereof. If the required amplification ratio is 1.0, the amplification section is unnecessary. However, the amplification section is provided for possible cases where the amplification ratio must be changed.
“1.0/(1+0.2 s)” of the excitation voltage generator represents the characteristic of operation for generation of the voltage for operating the exciter. Here, the amplification ratio is set to 1.0, and the time constant is set to 0.2 sec.
“100.0/(1+2.0 s)” of the exciter represents the operation of the exciter for generation of the excitation voltage Efd. The operation time constant is set to 2.0 sec, and the amplification ratio is set to 100.0.
“0.1 s/(1+0.5 s)” of the hunting prevention section represents the feedback characteristic for preventing occurrence of a hunting phenomenon, which would otherwise occur due to excessively high response speed of the output Efd of the exciter. The time constant and amplification factor are set to the values shown in the drawing.
Meanwhile, the PSS (power system stabilizer) is provided so as to generate an auxiliary signal for the exciter so as to stabilize the rotation of the generator; i.e., eliminate fluctuation in the rotation. As shown in the drawing, the PSS uses a change amount Δω of the rotational speed of the generator as an input, and its output is applied to the excitation apparatus as an auxiliary signal (Vpss). The PSS is composed of a signal amplifier for increasing the voltage level of the input Δω signal to the level of an operation signal of the excitation apparatus; a signal reset section for removing the DC deviation component from the signal; and signal phase compensators for adjusting the phase of the signal by advancing or delaying the phase to thereby stabilize the fluctuation (here, two signal phase compensators are used, for first and second signal phase adjustments).
The auxiliary signal, which is output from the PSS (power system stabilizer) on the basis of the input Δω, and is used to stabilize the fluctuation, is fed to the excitation voltage generator after being added to the signal 1.0×(Vref−Vt), which corresponds to the deviation of the voltage Vt from the prescribed value. Equations shown in the drawing represent the function of the PSS, which is actually realized by means of hardware such as a circuit board including semiconductors, etc. Similarly, in the case of the excitation apparatus as well, equations shown in the drawing represent the function of the apparatus, which is actually realized by means of hardware such as electromagnetic devices, a circuit board including semiconductors, etc.
“K/(1+T0s)” representing the operation of the signal amplifier of the PSS shows the response (response time constant T0) and signal amplification (amplification ratio K) of a detector for detecting the rotational angular speed change Δω of the generator. “Tωs/(1+Tωs)” of the signal reset section indicates that this section serves as a filter for canceling the offset component of the signal. “(1+T1s)/(1+T2s)” of the first signal phase adjustment section indicates that this section serves as a first signal phase compensator for adjusting the signal for fluctuation stabilization by advancing or delaying the phase of the signal. “(1+T3s)/(1+T4s)” of the second signal phase adjustment section indicates that this section plays the same role as the first signal phase adjustment section; i.e., this section serves as a second signal phase compensator which is connected in series to the first signal phase compensator so as to increase the amount of phase advance or delay.
A ΔP-type PSS employed in many generators currently operated is effective for suppression of local fluctuation. Further, in order to suppress long-period power fluctuation, a (ΔP+Δω)-type PSS is also employed in many generators, and the (ΔP+Δω)-type PSS is reported to be effective in increasing the amount of power that can be transmitted stably (see Non-Patent Document 1). In another example, a PSS compensator is configured such that an additional signal is input as a feedback signal so as to stabilize a plurality of modes including a long-period fluctuation mode (see Patent Document 2).
In a known technique, information regarding an electric power system is acquired from several points in the power system; the frequency, attenuation rate, and amplitude of a fluctuation are calculated from the waveform by use of Prony analysis, and the stability of the system is monitored through observation of the results of the analysis (see Patent Document 3). However, in this method, it is considered that waveform analysis must be performed after a certain clear disturbance. Therefore, it is desired to constitute an electric power system fluctuation model from a fluctuation of an electric power system in an ordinary state. Moreover, in this technique, power source restriction is employed as a measure for system stabilization. However, a guideline for design of the excitation control system is desired.
The present inventors have installed phase measurement devices with a time synchronization function at universities throughout Japan and established a system for observing the dynamic characteristic of the entire power system. On the basis of phase information obtained through the observation, a long-period fluctuation mode; in particular, one fluctuating throughout the entire system, can be extracted from a very small fluctuation in a steady state (see Non-Patent Document 2). Thus, adjusting the PSS in accordance with the extracted fluctuation is expected to effectively suppress an inter-system long-period fluctuation. Heretofore, there has been studied a method for adjusting a PSS on the basis of a combined vibration model configured from fluctuation observation in consideration of mutual action between modes (see Non-Patent Document 3). In this method, attempts have been made to investigate the direction of change of each mode by changing PSS parameters by very small amounts and adjust the PSS on the basis of the results of the investigation. In this method, each time that adjustment is performed, the model must be reconstituted and the parameters must be determined through trial and error.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H10-52096    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H11-206195    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2001-352679    Non-Patent Document 1: “Development of Plural PSSs Suppressing Long-Period Fluctuation of Linked System and Study on Fluctuation Model,” The transactions of the Institute of Electrical Engineers of Japan B. Vol. 115-B, No. 1, 1995    Non-Patent Document 2: Hashiguchi, et al.: “Identification of Characteristic Coefficients of Power Fluctuation Based on Multipoint Synchronized Phasor Amount Measurement,” Annual Conf. of Power and Energy Society of the Institute of Electrical Engineers of Japan, No. 204 (2004)    Non-Patent Document 3: Watanabe, et al.: “Power System Stabilization Control Based on Fluctuation Observation,” Paper of Workshop of the Institute of Electrical Engineers of Japan, PE-04-45, PSE-04-45 (2004)    Non-Patent Document 4: “Standard Model of Power System” edited by Expert Committee for Investigation for Power System Model Standardization, Technical Report No. 754 (1999) of the Institute of Electrical Engineers of Japan    Non-Patent Document 5: Moriyuki Mizumachi, “Short Article GPS (global positioning system) Technology and its Future Development,” Measurement and Control, 36, 8, pp. 533-562 (1997-8)    Non-Patent Document 6: Michito Imae, “Global Positioning System (GPS) and its Application,” The transactions of the Institute of Electrical Engineers of Japan B, Vol. 118, 3, pp. 227-230 (1998-3)    Non-Patent Document 7: R. Tsukui, P. Beaumont, T. Tanaka and K. Sekiguchi: “Intranet-Based Protection and Control,” IEEE Computer Applications in Power, pp. 14-17 (2001-4)    Non-Patent Document 8: The Math Workds: MATLAB Wavelet Toolbox, Wavelet Toolbox User's guideNon-Patent Document 9: Kazuyuki Kobayashi: MATLAB Handbook, Shuwa System (1998)    Non-Patent Document 10: Haruji Ohsawa and Hiroaki Sugihara: “Consideration on Stabilization Control of Power System Composed of a Large Number of Distributed Power Sources,” Paper of Workshop for Power Technology and Power System Technology of the Institute of Electrical Engineers of Japan, PE-98-116, PSE-98-106 (1998)